Flat-panel display devices are widely used in conjunction with computing devices, in portable electronic devices, and for entertainment devices such as televisions. Such flat-panel displays typically employ a plurality of pixels distributed over a substrate to display images. Each pixel incorporates several, differently colored light-emitting elements commonly referred to as sub-pixels, typically emitting red, green, and blue light, to represent each image element. Pixels and sub-pixels are not distinguished herein; all light-emitting elements are called pixels. A variety of flat-panel display technologies are known, for example plasma displays, liquid crystal displays, and light-emitting diode displays.
Light-emitting diodes (LEDs) incorporating thin films of light-emitting materials forming light-emitting elements have many advantages in a flat-panel display device and are useful in optical systems. One exemplary organic LED display device includes an array of organic LED light-emitting elements. Alternatively, inorganic materials can be employed and can include phosphorescent crystals or quantum dots in a polycrystalline semiconductor matrix. Other thin films of organic or inorganic materials can also be employed to control charge injection, charge transport, or charge blocking to the light-emitting-thin-film materials, and are known in the art. The thin-film materials are placed upon a-substrate between electrodes, with an encapsulating cover layer or plate. Light is emitted from a pixel when current supplied by the electrodes passes through the light-emitting material. The frequency of the emitted light is dependent on the nature of the material used. In such a display, light can be emitted through the substrate (a bottom emitter) or through the encapsulating cover (a top emitter), or both.
LED devices can include a patterned light-emissive layer wherein different materials are employed in the pattern to emit different colors of light when current passes through the materials. Alternatively, one can employ a single emissive layer, for example, a white-light emitter, together with color filters for forming a full-color display. It is also known to employ a white light-emitting element that does not include a color filter. A design employing an unpatterned white-light emitter has been described together with a four-color pixel comprising red, green, and blue color filters and sub-pixels and an unfiltered white sub-pixel to improve the efficiency of the device.
Typical display apparatuses range in size from small displays used in mobile devices to very large displays visible to thousands of viewers. Large displays can be provided by tiling smaller display devices together. For example, video walls using multiple video displays are frequently seen in the electronic media and flat-panel displays can be tiled to create larger displays. Multiple projector systems used to create a large, tiled, high-resolution display are also known.
Flat-panel tiled displays are well known in the prior art. Many flat-panel tiled display apparatuses employ rectangular display tiles with pixel arrays formed in display areas on the display tile. Each display tile has a separate substrate that is butted together at the edges with a separate display tile to form a single, flat surface. In such a configuration, it is important that the edge seams between the display tiles be imperceptible to a viewer and therefore do not have a reflectance or light emission that differs from the display area of the display tiles. Moreover, the gap between adjacent light-emitting pixels is the same over the butted tiled edges as it is between light-emitting pixels in the display area so that the pixels are uniformly distributed over the tiled array.
Various butted tiling methods employ tile structures fastened together into an array with the use of a frame or an electroluminescent display panel including multiple small-size panels secured to a larger support with an intervening adhesive layer. Alternatively, tiled display structures can include a plurality of display tiles mounted upon a back panel that are interconnected through electrical stand-off connectors or that include a plurality of display tiles mounted upon a back panel with electrode segments formed over electrode busses. Tiles attached to a mounting surface can emit light from one surface of the tile and conductors can be connected at a second surface. It is also known to use black-matrix material in a tiled display. A tiled display can locate all of the electronic circuitry beneath the pixel array. Vertical interconnects are made between the pixel electrodes and drive circuits, thereby enabling a seamless image. Optical structure that hide tile seams are also known in the art, for example by employing a distributed ultra-low magnification fly's-eye optical system integrated with the display tiles, effectively excluding and obscuring an image of the tile seams.
Generally, prior art methods for obscuring tile seams seek to reduce the tile perimeter width so that butted-together tiles have a common inter-pixel distance over the multiple tiles. In other approaches, the tile seam is made less visible, for example through optical structures, by controlling the pixels in the display tiles, or employing special tile cutting or encapsulation techniques. Other disclosures seek to ensure that the power distribution over the tiles is uniform.
It is difficult and expensive, however, to maintain a constant inter-pixel distance across the edge of two butted-together tiles. In particular, OLED devices require protection from environmental contamination, especially moisture. To avoid such contamination, OLED devices generally employ a hermetic seal around the perimeter of the display. This hermetic seal can cause the edge of a tile to be wider than the inter-pixel distance.
Another technique for reducing tile seam visibility relies on overlapping the display tiles. For example, U.S. Patent Publication 2006/0108915, now abandoned, discloses a tiled OLED display structure wherein OLED display tiles are stacked over non-display areas of other OLED display-tile substrates. Commonly-assigned U.S. Pat. No. 6,614,171 discloses a tiled display having tiles with spaced-apart edge pixels stacked upon a back-plate that includes pixels disposed between the spaced-apart display tile edge pixels. These structures employ multiple substrates, are not readily scalable, and are difficult to interconnect. Alternatively, WO2006023901 discloses an array of display tiles for which the edge seam width is reduced by overlapping the edge of the tiles so that a ribbon cable connector can extend beneath the overlap. Another approach is described in WO 2003/042966 and U.S. Pat. No. 7,362,046. This method uses a complex support structure and a plurality of printed circuit boards, on each of which is mounted a separate display with a separate substrate. The printed circuit boards are mounted at an angle to a viewing surface and the edge of each printed circuit board overlaps the edge of a neighboring printed circuit board. In a related disclosure, commonly assigned, co-pending U.S. Patent Publication 2007/0001927 describes an electronic signage system having a plurality of display elements wherein one display element overlaps another display element. These designs can overlap the tile edge of one tile with a neighboring tile, thereby reducing the tile seam width by one half. However, this reduction can be inadequate, especially for high-resolution displays with small inter-pixel distances, and still restricts the edge width of the display tiles. U.S. Patent Application 2009/0021162 describes a flexible emissive display that can include display tiles coupled to a flexible support but does not thereby reduce tile seam visibility.
There is a need, therefore, for an improved tiled display apparatus that overcomes the problems noted above.